This paper presents a magnetic sensor on thin-film SOI-SIMOX that takes advantage of a previous bipolar structure, the VCBM (voltage-controlled bipolar MOS transistor) to improve magnetic response with low power consumption. The buried oxide avoids substrate currents, while keeping a high relative sensitivity, up to 50% T−1, of the sensor. The paper introduces the structure and theoretical operation regions for both electric and magnetic features. Experimental results on two devices validate the previous analysis, presenting the main figures of merit. Finally, the total device efficiency parameter is introduced.